go.mod

module m

go 1.15

require (
	github.com/go-chi/chi v4.1.2+incompatible
	github.com/go-chi/render v1.0.1
	golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1
)

go.sum

github.com/go-chi/chi v1.0.0 h1:s/kv1cTXfivYjdKJdyUzNGyAWZ/2t7duW1gKn5ivu+c=
github.com/go-chi/chi v4.1.2+incompatible h1:fGFk2Gmi/YKXk0OmGfBh0WgmN3XB8lVnEyNz34tQRec=
github.com/go-chi/chi v4.1.2+incompatible/go.mod h1:eB3wogJHnLi3x/kFX2A+IbTBlXxmMeXJVKy9tTv1XzQ=
github.com/go-chi/render v1.0.1 h1:4/5tis2cKaNdnv9zFLfXzcquC9HbeZgCnxGnKrltBS8=
github.com/go-chi/render v1.0.1/go.mod h1:pq4Rr7HbnsdaeHagklXub+p6Wd16Af5l9koip1OvJns=
golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1 h1:go1bK/D/BFZV2I8cIQd1NKEZ+0owSTG1fDTci4IqFcE=
golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=

main.go

package main

import (
	"fmt"
	"log"
	"net/http"
	"os"

	"github.com/go-chi/chi"
	"github.com/go-chi/render"
	"golang.org/x/xerrors"
)

func main() {
	s := &Server{
		Router: chi.NewRouter(),
		logger: log.New(os.Stdout, "app", 0),
	}
	s.Mount()

	addr := os.Getenv("Addr")
	if addr == "" {
		addr = ":4444"
	}

	log.Printf("listen: %s", addr)
	if err := http.ListenAndServe(addr, s); err != nil {
		log.Fatalf("!! %+v", err)
	}
}

type logger interface {
	Printf(string, ...interface{})
}

type Server struct {
	logger logger
	chi.Router
}

func (s *Server) Mount() {
	s.Get("/500", func(w http.ResponseWriter, r *http.Request) {
		err := f()
		if err != nil {
			s.logger.Printf("! %+v", err)
			render.Status(r, 500)
			render.JSON(w, r, map[string]string{"error": fmt.Sprintf("%v", err)})
			return
		}
		render.JSON(w, r, map[string]string{"message": "never"})
	})
}

func f() error {
	err := g()
	return xerrors.Errorf("f %w", err)
}
func g() error {
	err := h()
	return xerrors.Errorf("g %w", err)
}
func h() error {
	return fmt.Errorf("h")
}

main_test.go

package main

import (
	"fmt"
	"io"
	"net/http"
	"net/http/httptest"
	"os"
	"testing"

	"github.com/go-chi/chi"
)

type testlogger struct {
	testing.TB
}

func (tl *testlogger) Printf(fmt string, args ...interface{}) {
	tl.Helper()
	tl.Logf("\x1b[90m"+fmt+"\x1b[0m", args...)
}

func TestIt(t *testing.T) {
	s := &Server{
		Router: chi.NewRouter(),
		logger: &testlogger{TB: t},
	}
	s.Mount()

	ts := httptest.NewServer(s)
	defer ts.Close()

	res, err := http.Get(fmt.Sprintf("%s/500", ts.URL))
	if err != nil {
		t.Fatalf("unexpected %v", err)
	}

	if res.StatusCode != 200 {
		t.Errorf("want 200 but %d", res.StatusCode)
	}

	fmt.Println("----------------------------------------")
	fmt.Print("response: ")
	io.Copy(os.Stderr, res.Body)
	fmt.Println("----------------------------------------")
	defer res.Body.Close()
}